1. Field of the Invention
The invention relates to a self-washing device for separating and filtering solid particles from a flow of liquid, and to the use of the device in a fuel injection circuit.
2. Description of the Prior Art
In many systems using high pressure liquids, the liquid must be thoroughly filtered to prevent wear due to contaminants present in the liquid. Conventionally this requirement is met by a filter cartridge which can be replaced when it is clogged. It is also conventional to provide a by-pass valve through which the liquid can flow when the filter cartridge is clogged. The state of the filter must therefore be checked regularly to prevent rapid deterioration of the costly equipment which the filter is intended to protect.
In the particular case of a system for feeding and metering the fuel in a turbomachine, the system including a gear pump, for example of the positive displacement kind, a flow-metering device and fuel injectors, it is necessary to protect the system from external contamination originating from the fuel tanks and to protect the metering device and injectors from contamination by wear particles produced by and possibly even damaging the pump. However, this double protection cannot be provided by a single filter. Also, the use of two filters placed one upstream and one downstream of the pump makes installation difficult, increases engine weight , requires additional maintenance operations and makes operation difficult due to the high pressures downstream of the pump. Furthermore, these systems introduce appreciable pressure drops which increase proportionally as the filter becomes increasingly clogged.
To avoid the problem of having to maintain the filter disposed downstream of the pump, a self-washing filter can be used. Known self-washing filters usually comprise a filter cartridge having a central duct through which the main proportion of the fuel flow passes. To supply the fuel metering and fuel injection devices some of the fuel is drawn from the central duct of the filter and filtered through the filter cartridge. The disadvantage of these known self-washing filters is that in order for the washing to be effective they can filter only a small proportion of the total fuel flow entering the filter. The filtered fuel flow is usually less than 10% of the total fuel flow entering the filter. Consequently, the greater the fuel flow to be filtered is, the greater the filter cartridge area must be. The known self-washing filters therefore tend to be heavy and bulky.